Abstract: Collapse of concrete buildings has elicited various researches on the quality of construction materials. Fine aggregates such as sand used in concrete production may contain excessive silt and clayey contents as well as organic impurities that impact negatively on the quality of hardened concrete. The objective of this research was to establish level of silt and clay content and organic impurities in building sand and its effect on bond strength of concrete. This paper presents the findings on the quality of building sand as sourced from eight supply points in Nairobi City County and its environs and the effects of sand impurities on the bond strength of concrete through the pull out test method to assess contribution of these impurities to the frequent collapse of buildings occurring in Kenya. Sieve analysis, specific gravity test, testing for silt and clay content and organic impurities were carried out as detailed in BSS 882, IS and ASTM standards. In casting of concrete specimens, the quality of cement, course aggregates (crushed stones), water and reinforcement bar were held constant while sand with varying level impurities and varying sources. The results showed that 86.2% and 50% of tested samples exceeded the allowable limits for silt and clay content and organic content respectively. It was observed that bond strength between concrete and reinforcement bars decreased with increase in silt and clay content while it increased and then decreased with increase in organic impurities. Predictive regression equations were generated showing development of bond strength with varying levels of silt and clay, and organic impurities of building sand respectively. It is concluded that presence of these impurities in sand decreases the bond strength between concrete and reinforcement bars hence play a role in lowering the structural integrity of buildings. The research established that particle sizes, shape, texture and workability play an important role in determination of compressive strength of concrete.
Keywords: sand quality, silt and clay content, organic impurities, pull out force, bond strength, buildings failure.
Title: EFFECTS OF SAND QUALITY ON BOND STRENGTH OF CONCRETE: A CASE STUDY IN NAIROBI CITY COUNTY AND ITS ENVIRONS, KENYA
Author: H. N. Ngugi, R. N. Mutuku, Z. A. Gariy
International Journal of Civil and Structural Engineering Research
ISSN 2348-7607 (Online)
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